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Screenshot of 2024-10-20.jpg (113,253 bytes) Screenshot of 2025-10-20.jpg (101,160 bytes) |
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Your screenshot show the astrometry from Hipparcos, if you upgrade to the beta version 4.3 it include the new measurement from GAIA. This is this values I use below. You probably forget to multiply by the cosine of the declination. For 61 Cyg A, with the date you mention I get for RA: (21.117535-21.117436)*15*3600*1000*cos(38.77) = 4169 The indicated ra proper motion is 4164.210 Also the reported value of the ra proper motion is valid only at GAIA epoch 2016.0. It change over time as we pass by this two stars. To take account for that CdC compute the proper motion in 3D space, not only in the tangential plane, using also the parallax and radial velocity. You can look at the code here: https://github.com/pchev/skychart/blob/master/skychart/u_projection.pas#L1070 |
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Thank you, Patrick, for pointing out my mistake about the cosine of the declination. I'm in the process of upgrading, but I am actually trying to measure the parallax of 61 Cyg and have a large number of photographs which I am processing. So I think I may have to retain the old version for consistency. |
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Sure you can keep the version 4.2, Hipparcos data is good too. |
- Anonymous
